I trim the breech end only to set the shank length for aesthetics and stock fit. If looks are less important than length, or if I'm utilizing one of my various 'pull-down tuners' I'll pretty much face the back off leaving the entire shank (I actually go thru the trouble of parting it off generally because for some stupid reason I keep the stamped end in my build-record envelope) and drill/bore ignoring the lapping bell. I run in and map the first 6"-7" of the bore trying to get a feel for how it takes off from the breech end so even with the lapping bell left on I've plenty of clean bore to work with.
If the muzzle wants to finish out long, near the bell, I'll generally upset a lead plug and do a quik-N-dirty tightness check of the muzzle end. Of course on some guns I slug it righteous in which case the lapping bells are kinda' handy to catch and return the slug.